Physics 9702 · AS & A Level · Resistance and resistivity
Resistance and resistivity — practice question
A heater is being made from nichrome wire. At the heater’s operating temperature, nichrome has a resistivity of $1.0 \times 10^{-6}\,\Omega\,\text{m}$. The heater must dissipate $60\,\text{W}$ when the potential difference across its terminals is $12\,\text{V}$.
(a(i))[2]
Calculate the current for the heater operating at its intended power output.
(a(ii))[2]
Show that the nichrome wire has a resistance of $2.4\,\Omega$.
(b)[3]
Calculate the length of nichrome wire with diameter $0.80\,\text{mm}$ needed for the heater.
(c)[3]
A second heater, also intended to run from a $12\,\text{V}$ supply, is made from the same nichrome wire but with half the length calculated in (b). Explain quantitatively how this change in wire length affects the heater’s power.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “$P = VI$” …